Iron alloy electrode paste and preparation process

Abstract

The invention discloses an iron alloy electrode paste and a preparation process, and belongs to the technical field of electrode paste preparation, the iron alloy electrode paste comprises a composite aggregate system and a composite binder system, the composite aggregate system comprises the following components by mass: 40-60% of anthracite aggregate, 15-25% of artificial graphite flake, and 3-8% of silicon carbide whisker; the composite binder system comprises the following components in percentage by mass: 70-80% of medium-temperature modified coal pitch, 10-15% of furan resin and 5-10% of dispersion liquid containing nano boron carbide, and the composite binder system is combined with the composite aggregate system through a gradient permeation process to form a three-dimensional conductive network and an enhanced interface; the composite aggregate system and the composite binder system are optimally proportioned, and gradient permeation and gradient kneading processes are combined, so that the comprehensive performance of the electrode paste is remarkably improved, the thermal shock resistance is greatly improved and the linear shrinkage rate is reduced while low resistivity is maintained, the electrode paste is suitable for smelting ferroalloys such as silicomanganese and ferrochromium, and the service life is remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of electrode paste preparation technology, specifically to an iron alloy electrode paste and its preparation process. Background Technology

[0002] With the continuous development of submerged arc furnace technology, especially the advancement towards higher power, the requirements for electrode paste have also increased. Existing ferroalloy electrode pastes mainly rely on anthracite and petroleum coke as aggregates and coal tar pitch as a binder. While this combination can guarantee the basic performance of the electrode paste to a certain extent, several significant technical challenges remain. First, a single aggregate system can improve the conductivity of the electrode paste, but its thermal shock resistance is low, typically only able to withstand fewer than five thermal shock cycles. To improve thermal shock resistance, the conductivity of the electrode paste needs to be reduced, making it difficult to achieve a balance between the two, thus limiting the application of the electrode paste. Second, traditional coal tar pitch, due to its high viscosity, is difficult to fully wet the micropores of the aggregate, causing the nano-reinforcing phase to easily agglomerate during use, with a dispersion efficiency of only about 30%, thus affecting the overall performance of the electrode paste. Furthermore, the isothermal kneading process results in disordered aggregate arrangement, leading to a shrinkage rate of the electrode paste that is typically greater than 0.8% during rapid sintering, easily generating thermal stress cracks, further reducing the mechanical strength and service life of the electrode paste.

[0003] To address these issues, researchers attempted to improve the electrode paste's performance by adding silicon carbide particles or using mixed aggregates. While these methods can improve conductivity and thermal shock resistance to some extent, they do not completely resolve the aforementioned contradictions. Adding silicon carbide particles can enhance conductivity, but it places a greater emphasis on improving thermal shock resistance, failing to effectively alleviate this problem. Simultaneously, the agglomeration of the nano-reinforcing phase persists, resulting in low dispersion efficiency. Furthermore, the shrinkage rate of the electrode paste during rapid sintering is difficult to control, causing significant shrinkage even during high-speed sintering, leading to cracks and affecting its performance.

[0004] In summary, there is an urgent need for a ferroalloy electrode paste and its preparation process that can significantly improve thermal shock resistance and reduce shrinkage while maintaining low resistivity. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned technical difficulties and provide an iron alloy electrode paste and its preparation process that can significantly improve thermal shock resistance and reduce shrinkage while maintaining low resistivity.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A ferroalloy electrode paste, comprising a composite aggregate system and a composite binder system, wherein the composite aggregate system comprises the following components by mass percentage: 40-60% anthracite aggregate, 15-25% artificial graphite flakes, and 3-8% silicon carbide whiskers; the composite binder system comprises the following components by mass percentage: 70-80% medium-temperature modified coal tar pitch, 10-15% furan resin, and 5-10% dispersion containing nano-boron carbide; the composite binder system is combined with the composite aggregate system through a gradient infiltration process to form a three-dimensional conductive network and a reinforced interface.

[0007] Furthermore, the anthracite aggregate is calcined in air at 1200-2000℃ to form a microporous layer with a pore size of 0.5-2μm and a porosity of 15-25% on its surface.

[0008] Furthermore, the artificial graphite flakes have a diameter of 0.1-0.5 mm and an orientation angle of ≤30° in the electrode paste, the silicon carbide whiskers have an aspect ratio of 20:1-50:1, and the length of the silicon carbide whiskers is ≤ the diameter of the artificial graphite flakes.

[0009] Furthermore, the softening point of the medium-temperature modified coal tar pitch is 85-95℃, and the content of quinoline insoluble matter is ≤8%.

[0010] Furthermore, the surface of the boron carbide nanoparticles in the boron carbide nanoparticle dispersion is coated with a polyacrylate dispersant, with a dispersed solids content of 15-25 wt%.

[0011] Furthermore, a process for preparing the iron alloy electrode paste includes the following steps: 1) Aggregate pretreatment: preheat anthracite aggregate, artificial graphite flakes, and silicon carbide whiskers at 80-100℃ for 30-60 minutes; 2) Binder premixing: The total amount of nano boron carbide dispersion is premixed with 20% of the total amount of medium-temperature coal tar pitch and treated under ultrasonic conditions of 120℃ and 40KHz for 25 minutes to obtain a homogeneous premixed solution without agglomeration. 3) Gradient kneading: In the first stage, furan resin is added to the preheated aggregate and kneaded for 10-15 minutes at 80-100℃ and 20-30 rpm. In the second stage, add the remaining medium-temperature modified coal tar pitch and the premixed liquid from step (2), heat to 130-150℃, and knead at 40-50 rpm for 15-20 minutes. The third stage involves heating to 180-200℃ and kneading at 60-70 rpm for 5-10 minutes to homogenize the exhaust gas. 4) Molding and cooling: The mixed material is extruded and cooled to below room temperature to obtain the finished electrode paste.

[0012] Furthermore, the gradient kneading described in step 3) is carried out in a double-helix variable-diameter kneader, with a speed ratio of 1:3 between the main helix and the auxiliary helix, a length-to-diameter ratio of ≥8:1 for the kneader, a diameter ratio of 2:1 between the main helix and the auxiliary helix, and a helix blade inclination angle of 15-25°.

[0013] Furthermore, in the second stage of step 3), the nano boron carbide dispersion and the medium-temperature modified coal tar pitch are premixed at a mass ratio of 1:3-5 under ultrasonic conditions at 120℃ and 40KHz for 20-30 minutes.

[0014] Furthermore, the electrode paste prepared by the electrode paste or the process described above is sintered and is suitable for smelting silicon-manganese alloy or ferrochrome alloy. After sintering, the bulk density is ≥1.65g / cm³ and the resistivity is ≤55μΩ·m.

[0015] The iron alloy electrode paste and its preparation process provided by this invention have the following beneficial effects: This application provides a ferroalloy electrode paste and its preparation process. By optimizing the ratio of the composite aggregate system and the composite binder system, and combining gradient infiltration and gradient kneading processes, the overall performance of the electrode paste is significantly improved. While maintaining low resistivity, it greatly enhances thermal shock resistance and reduces linear shrinkage, and has high bulk density and compressive strength. It is suitable for smelting ferroalloys such as silicon manganese and ferrochrome, and its service life is significantly extended. Attached Figure Description

[0016] Figure 1 This is a schematic diagram showing the composition and proportions of the iron alloy electrode paste of the present invention.

[0017] Figure 2 This is a schematic diagram of the process flow for preparing the ferroalloy electrode paste of the present invention.

[0018] Figure 3 This is a schematic diagram of the twin-helix structure of the twin-helix mixer used in the preparation process of the ferroalloy electrode paste of this invention. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Example 1 like Figure 1-2The present invention provides a ferroalloy electrode paste, comprising, by weight (100%), a composite aggregate system of 72% and a composite binder system of 28%. The composite aggregate system comprises the following components by weight percentage: 40-60% anthracite aggregate, which is pre-treated and crushed to 2-8mm particles, and then calcined in air at 1200-2000℃ to form a microporous layer with a pore size of 0.5-2μm and a porosity of 15-25%; 15-25% artificial graphite flakes, with a thickness of 5-10μm, a flake diameter of 0.1-0.5mm, and an orientation angle ≤30° in the electrode paste; and 3-8% silicon carbide whiskers, with a diameter of 0.5-1μm, a length of 15-45μm, and an aspect ratio of 20:1-50:1. The length of the silicon carbide whiskers is ≤ the diameter of the artificial graphite flakes. The composite binder system comprises the following components by mass percentage: 70-80% medium-temperature modified coal tar pitch with a softening point of 85-95℃ and a quinoline insoluble content of ≤8%; 10-15% furan resin with a solid content of >95%; and 5-10% dispersion containing nano-boron carbide, wherein the nano-boron carbide particles have a particle size of 50-80nm, the dispersion has a solid content of 20wt%, and the nanoparticles are coated with polyacrylate dispersant.

[0021] This application preferably uses a composite aggregate system consisting of 47% anthracite aggregate, 20% artificial graphite flakes, and 5% silicon carbide whiskers. The composite binder system is composed of the following components, with each component accounting for a percentage of the total electrode paste and its proportion in the binder system: 21% medium-temperature modified coal tar pitch, which accounts for 21 / 28=75% of the binder system weight; 4.2% furan resin, which accounts for 4.2 / 28=15% of the binder system weight; and 2.8% dispersion containing nano-boron carbide, which accounts for 2.8 / 28=10% of the binder system weight.

[0022] This application uses the process of Example 2 to prepare the above formula into electrode paste, and after sintering, the performance is tested. The test results are as follows: bulk density: 1.67 g / cm³, resistivity: 53 μΩ·m, thermal shock resistance (water cooling cycle): no cracking after 17 cycles, linear shrinkage rate: 0.45%, compressive strength: 27 MPa.

[0023] Comparative Example 1 Based on the above embodiments, this comparative example increases the proportion of furan resin to 5.6% (accounting for 20% of the binder system), exceeding the upper limit of 10-15% of the present invention. Correspondingly, the proportion of medium-temperature coal tar pitch is reduced to 19.6% (accounting for 70% of the binder system), while the proportion of nano-dispersion remains unchanged. This comparative example uses the process of Example 2 to prepare the above formula into an electrode paste, and after sintering, performance tests show that its resistivity increases to 61 μΩ·m, and its thermal shock resistance decreases to 13 cycles. Through experimental testing and comparative analysis, it is found that excessive furan resin prematurely undergoes condensation and solidification during the low-temperature kneading stage, severely hindering the deep wetting and uniform spreading of medium-temperature coal tar pitch into the aggregate micropores in the subsequent high-temperature stage, resulting in uneven binder distribution, forming conductive defects and stress concentration points.

[0024] Comparative Example 2 Based on the above embodiments, this comparative example omits the boron carbide nano-dispersion and replaces it with an equal amount of ordinary conductive carbon black, accounting for 2.8% of its mass. This comparative example uses the process of Example 2 to prepare the above formulation into an electrode paste. After sintering, performance testing revealed that the product's thermal shock resistance decreased sharply to 9 cycles, and the linear shrinkage rate increased to 0.7%. Comparative analysis showed that while ordinary carbon black provides conductivity, its nanoscale reinforcing and toughening effects (such as pinning, crack deflection, and bridging) are far inferior to those of high-hardness, high-modulus boron carbide (B4C) nanoparticles. B4C nanoparticles can more effectively suppress matrix shrinkage and crack propagation during sintering.

[0025] Comparative Example 3 Based on the above embodiments, this comparative example reduces the proportion of nano-boron carbide dispersion to 1.4% (5% of the binder system) while increasing the proportion of medium-temperature coal tar pitch to 22.4% (80% of the binder system). This comparative example uses the process of Example 2 to prepare the above formulation into an electrode paste, and after sintering, performance testing shows that its thermal shock resistance decreased to 14 cycles. Comparative analysis based on experimental testing indicates that the nano-phase content is insufficient to form a continuous and effective reinforcing network in the binder matrix, and is insufficient to significantly inhibit crack initiation and propagation under thermal stress.

[0026] In summary, the formulation provided in this application, when produced according to the preparation process of Example 2, produces a finished electrode paste that can significantly improve thermal shock resistance and reduce shrinkage while maintaining low resistivity.

[0027] Example 2 Based on the above embodiments, this embodiment provides a preparation process for the iron alloy electrode paste, using a double-spiral variable-diameter mixer, such as... Figure 3The described double-helix variable-diameter kneader has a length-to-diameter ratio of 10:1, a main helix diameter of 400mm / secondary helix of 200mm, a blade inclination angle of 20°, and a speed ratio of 1:3. The double-helix variable-diameter kneader of this invention adopts a parallel double-shaft design with opposite-direction and differential rotation. The helical blades are intermeshing with each other, which can generate strong shearing, squeezing and kneading effects during rotation, thereby ensuring that the material is fully mixed. The main helix of this application is mainly responsible for conveying and macroscopic mixing, while the high-speed rotating secondary helix provides strong shearing force to achieve microscopic dispersion and homogenization.

[0028] Its preparation process includes the following steps: 1) Aggregate pretreatment: preheat anthracite aggregate, artificial graphite flakes, and silicon carbide whiskers at 80-100℃ for 30-60 minutes to remove moisture and reduce viscosity during subsequent kneading.

[0029] 2) Binder premixing: The entire amount of nano boron carbide dispersion is premixed with 20% of the total amount of medium-temperature coal tar pitch and treated under ultrasonic conditions of 120℃ and 40KHz for 25 minutes to obtain a homogeneous premixed solution without agglomeration.

[0030] 3) Gradient kneading: In the first stage, furan resin is added to the preheated aggregate. That is, the preheated aggregate is put into the kneader, all the furan resin is added, and kneading is carried out at 80-100℃ and 20-30rpm for 10-15min. In this application, the temperature is controlled at 90±2℃, the main screw is 25rpm, the torque is 18N·m, and the indicators are monitored in real time. The contact angle of the anthracite aggregate surface is ≤30° by the video contact angle meter. The low viscosity and high wettability of furan resin are utilized to preferentially penetrate into the pores of the aggregate, creating a channel for the subsequent introduction of high viscosity coal tar pitch.

[0031] In the second stage, the remaining medium-temperature modified coal tar pitch and the premixed liquid from step (2) are added, and the temperature is raised to 130-150℃. The mixture is kneaded at 40-50 rpm for 15-20 min. Further, the nano boron carbide dispersion and the medium-temperature modified coal tar pitch are premixed at a mass ratio of 1:3-5 under ultrasonic conditions at 120℃ and 40KHz for 20-30 min. In this application, the temperature in the second stage is controlled at 140±5℃, the main screw is 45 rpm, the torque is 35 N·m, and the indicators are monitored in real time. The viscosity of the mixture is monitored by an online viscometer and found to be 0.25±0.05 Pa·s. The temperature in this stage reduces the viscosity of the coal tar pitch, achieving full bonding with the aggregate. The rotation speed is increased to apply sufficient shear force to ensure uniform dispersion of nanoparticles and break up soft agglomerates.

[0032] In the third stage, the temperature is raised to 180-200℃, and the mixture is kneaded at 60-70 rpm for 5-10 minutes to homogenize the exhaust gas. In this application, the temperature in the third stage is controlled at 190±5℃, the main screw is at 65 rpm, the torque is 12 N·m, and the indicators are monitored in real time. The volatile content is ≤0.8% as detected by online gas chromatography. In this stage, under high temperature and low viscosity, the graphite flakes are oriented along the shear direction by high speed shear force, while the volatiles in the system are completely eliminated.

[0033] 4) Molding and cooling: The mixed material is extruded under a pressure of 15MPa and cooled to below room temperature to obtain the finished electrode paste.

[0034] Comparative Example 4 Based on Example 2 above, this comparative example uses the formula of Example 1, but eliminates the gradient kneading process. All aggregates and all binders are added to the kneader at one time and kneaded at a constant temperature of 140°C and 45 rpm for 38 minutes. This comparative example uses the formula of Example 1 to prepare electrode paste according to the above preparation process. After sintering, the performance test shows that its resistivity is 66 μΩ·m, thermal shock resistance is 10 cycles, and linear shrinkage rate is 0.75%, indicating a significant overall deterioration in performance. Through experimental testing and comparative analysis, it was found that low temperature cannot achieve preferential wetting of furan resin, and the simultaneous addition of high-viscosity coal tar pitch and nanoparticles leads to dispersion difficulties, agglomeration, incomplete removal of volatiles, and disordered orientation of graphite flakes.

[0035] Comparative Example 5 Based on Example 2 above, this comparative example uses the formulation of Example 1. When preparing the binder premix, ultrasonic treatment is omitted, and mechanical stirring is used only for 25 minutes. This comparative example uses the formulation of Example 1 to prepare electrode paste according to the above preparation process. After sintering, the performance test shows that its thermal shock resistance decreased to 14 cycles. SEM shows that there are obvious agglomerates of boron carbide nanoparticles. Through experimental testing and comparative analysis, it is found that the shear force of mechanical stirring cannot effectively break the soft agglomerates of nanoparticles, resulting in uneven distribution of the reinforcing phase, which becomes a crack source.

[0036] Comparative Example 6 Based on Example 2 above, this comparative example uses the formula of Example 1. After completing the second stage of kneading, the material is directly discharged, and the third stage is cancelled. This comparative example uses the formula of Example 1 to prepare electrode paste according to the above preparation process. After sintering, the performance test shows that its linear shrinkage rate increased to 0.62%. Through experimental testing and comparative analysis, it was found that the small molecule volatiles in the binder were not fully removed before molding. They escaped when heated during the subsequent sintering process, resulting in pores and microcracks in the product and poor dimensional stability.

[0037] The results of testing and comparing the electrode paste prepared by combining the optimal formula in Example 1 of this application with the preparation process in Example 2 with the traditional commercial electrode paste are shown in Table 1. Performance indicators This invention Traditional electrode paste Performance improvement Resistivity (μΩ·m) 53 78 -32% Thermal shock resistance (secondary) 17 5 +240% Linear shrinkage rate (%) 0.45 0.85 -47% Compressive strength (MPa) 27 18 +50% Table 1. Comparison of performance testing results of the present invention and traditional electrode paste. Therefore, it can be seen that the gradient kneading process designed in this application is far superior to the conventional process.

[0038] The ferroalloy electrode paste provided in Embodiment 1 of this application is prepared according to the preparation process of Embodiment 2, and its performance is compared with that of a traditional electrode paste. This includes volume density testing according to GB / T24525 (drainage method), resistivity testing according to GB / T24521 (four-probe method), thermal shock resistance testing according to YB / T118, linear shrinkage rate testing using a high-temperature dilatometer according to GB / T3074.5, and compressive strength testing at room temperature according to GB / T1431. The volume density of the electrode paste in this application is 1.67 g / cm³. 3 It has a resistivity of 53 μΩ·m, exhibits no cracking after 17 thermal shocks, a linear shrinkage rate of 0.45%, and a compressive strength of 27 MPa; the bulk density of the traditional electrode paste is 1.58 g / cm³. 3 The resistivity is 78 μΩ·m, the thermal shock resistance is 5 times cracking, the linear shrinkage rate is 0.85%, and the compressive strength is 18 MPa. It can be seen that the electrode paste prepared according to the above preparation process of this application has significant improvement in performance compared with the electrode paste prepared by the traditional process.

[0039] Example 3 Based on the above embodiments, this embodiment uses the formula described in Embodiment 1 and the electrode paste prepared by the process described in Embodiment 2. The electrode paste is then applied in a ferromanganese alloy submerged arc furnace for actual sintering. After sintering, the electrode paste is tested and found to have a bulk density ≥1.65g / cm³ and a resistivity ≤55μΩ·m, which fully meets the stringent requirements of high-power submerged arc furnaces for low resistance, high density and high thermal shock resistance of electrode materials. It is suitable for smelting ferroalloys such as ferromanganese and ferrochrome, and its service life is significantly extended compared to traditional electrodes.

[0040] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0041] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A ferroalloy electrode paste, characterized in that, The composite aggregate system comprises a composite aggregate system and a composite binder system. The composite aggregate system includes the following components by mass percentage: 40-60% anthracite aggregate, 15-25% artificial graphite flakes, and 3-8% silicon carbide whiskers. The composite binder system includes the following components by mass percentage: 70-80% medium-temperature modified coal tar pitch, 10-15% furan resin, and 5-10% dispersion containing nano-boron carbide. The composite binder system is combined with the composite aggregate system through a gradient infiltration process to form a three-dimensional conductive network and a reinforced interface.

2. The ferroalloy electrode paste according to claim 1, characterized in that: The anthracite aggregate is calcined in air at 1200-2000℃ to form a microporous layer with a pore size of 0.5-2μm and a porosity of 15-25% on its surface.

3. The ferroalloy electrode paste according to claim 1, characterized in that: The artificial graphite flakes have a diameter of 0.1-0.5 mm and an orientation angle of ≤30° in the electrode paste. The silicon carbide whiskers have an aspect ratio of 20:1-50:1 and the length of the silicon carbide whiskers is ≤ the diameter of the artificial graphite flakes.

4. The ferroalloy electrode paste according to claim 1, characterized in that: The softening point of the medium-temperature modified coal tar pitch is 85-95℃, and the content of quinoline insoluble matter is ≤8%.

5. The ferroalloy electrode paste according to claim 1, characterized in that: The surface of the boron carbide nano-dispersion is coated with polyacrylate dispersant, and the content of dispersed solids is 15-25 wt%.

6. A process for preparing the ferroalloy electrode paste according to any one of claims 1-5, characterized in that: Includes the following steps: 1) Aggregate pretreatment: preheat anthracite aggregate, artificial graphite flakes, and silicon carbide whiskers at 80-100℃ for 30-60 minutes; 2) Binder premixing: The total amount of nano boron carbide dispersion is premixed with 20% of the total amount of medium-temperature coal tar pitch and treated under ultrasonic conditions of 120℃ and 40KHz for 25 minutes to obtain a homogeneous premixed solution without agglomeration. 3) Gradient kneading: In the first stage, furan resin is added to the preheated aggregate and kneaded for 10-15 minutes at 80-100℃ and 20-30 rpm. In the second stage, add the remaining medium-temperature modified coal tar pitch and the premixed liquid from step (2), heat to 130-150℃, and knead at 40-50 rpm for 15-20 minutes. The third stage involves heating to 180-200℃ and kneading at 60-70 rpm for 5-10 minutes to homogenize the exhaust gas. 4) Molding and cooling: The mixed material is extruded and cooled to below room temperature to obtain the finished electrode paste.

7. A process for preparing the ferroalloy electrode paste according to claim 6, characterized in that: The gradient kneading described in step 3) is carried out in a double-helix variable-diameter kneader, with a speed ratio of 1:3 between the main helix and the auxiliary helix, a length-to-diameter ratio of ≥8:1 between the kneader and the auxiliary helix, a diameter ratio of 2:1 between the main helix and the auxiliary helix, and a helix blade inclination angle of 15-25°.

8. A process for preparing the ferroalloy electrode paste according to claim 6, characterized in that: In the second stage of step 3), the nano boron carbide dispersion and the medium-temperature modified coal tar pitch are premixed at a mass ratio of 1:3-5 under ultrasonic conditions at 120℃ and 40KHz for 20-30 minutes.

9. An electrode for a submerged arc furnace, characterized in that: The electrode paste prepared by any one of claims 1-5 or by any one of claims 6-9 is sintered and is suitable for smelting silicon-manganese alloy or ferrochrome alloy. After sintering, the bulk density is ≥1.65g / cm³ and the resistivity is ≤55μΩ·m.

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